This invention relates to a gyroscope suitable sensing rate on at least two axes, and preferably on three axes.
Vibrating structure gyroscopes may be fabricated using a variety of different structures as the resonant element. These include beams, tuning forks, cylinders, hemispherical shells and rings. Successful commercial exploitation is dependent upon optimising the device performance while minimising the cost. An additional goal for some applications is reducing the size of the device.
Some conventional vibrating structure gyro designs are suitable for fabrication using modern micro-machining techniques. These may be constructed from bulk Silicon, polysilicon or electro-formed metal. These fabrication methods provide the capability of producing miniature gyros in high volume and at reduced cost.
Many applications for gyroscopic devices require rate sensitivity about all three axes. Conventional vibrating structure gyros provide single axis rate sensitivity and therefore three devices are required which must be aligned along orthogonal axes. A vibrating structure gyro incorporating a resonator design which is inherently capable of sensing around three axes simultaneously would therefore be of great benefit. A single device would thus replace three conventional single axis units with obvious cost benefits. Also, the process of mounting and aligning the three single axis gyros would not be required.
There is thus a need for an improved gyroscope which can sense rate on at least two axes.
According to a first aspect of the present invention there is provided a gyroscope for sensing rate on at least two axes, including a substantially planar vibratory resonator having a substantially ring or hoop-like shape structure with inner and outer peripheries extending around a common axis, carrier mode drive means for causing the resonator to vibrate in a Cos n1xcex8 in-plane carrier mode, where n1 has an integer value of 2 or more, support means for flexibly supporting the resonator and for allowing the resonator to vibrate, in response to the carrier mode drive means, relative to the support means, carrier mode pick-off means for sensing in-plane movement of the resonator, X axis response mode pick-off means for sensing out-of-plane Cos nxcex8 response mode movement of the resonator in respect to rotation of the gyroscope around the X axis, where n has a value of n1+1 or n1xe2x88x921, and Y axis response mode pick off means for sensing out-of-plane Sin nxcex8 response mode movement of the resonator in respect to rotation of the gyroscope about the Y axis, where n has a value of n1+1 or n1xe2x88x921, identical to that for the X axis response mode.
Preferably, the gyroscope includes X axis response mode drive means for nulling the X axis response mode movement of the resonator to permit the gyroscope to be operated in a forced feedback configuration.
Conveniently, the gyroscope includes Y axis response mode drive means for nulling the Y axis response mode movement of the resonator to permit the gyroscope to be operated in a forced feed back configuration.
Advantageously, for sensing rate about two axes the support means includes a plurality of flexible legs flexibly connecting the resonator to a support, with the number of legs NT being given by NT=4 n and with the angular separation between the legs being given by 360xc2x0/NT.
Preferably, for sensing rate about three axes the gyroscope includes Z axis response mode pick off means for sensing in-plane Sin n1xcex8 response mode movement of the resonator in respect to rotation of the gyroscope around the Z axis, where n1 has an integer value of 2 or more, identical to that for the in-plane carrier mode.
Conveniently, the gyroscope for sensing rate about three awes includes Z axis response mode drive means for nulling the Z axis response mode movement of the resonator to permit the gyroscope to be operated in a forced feedback configuration.
Advantageously, the support means includes a plurality of flexible legs flexibly connecting the resonator to a support, with the number of legs NT being given by NT=4 nn1 and with the angular separation between the legs being given by 360xc2x0/NT.
Preferably, in a gyroscope of the present invention for sensing rate about two axes the carrier mode is an in-plane Cos 2 xcex8 mode, with the carrier mode drive means including two drive elements, for initiating the carrier mode motion, located at 0xc2x0 and 180xc2x0 with respect to a fixed reference axis in the plane of the resonator, with the carrier mode pick off means including two pick off elements, for detecting the carrier mode motion, located at 90xc2x0 and 270xc2x0 with respect to the fixed reference axis, wherein the X axis response mode is a Cos 3 xcex8 mode, with the X axis pick off means including three pick off elements located at 0xc2x0, 120xc2x0, and 240xc2x0 with respect to the fixed reference axis, with the X axis drive means including three drive elements located at 60xc2x0, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis, and wherein the Y axis response mode is a Sin 3 xcex8 mode, with the Y axis pick off means including three pick off elements located at 30xc2x0, 150xc2x0 and 270xc2x0 with respect to the fixed reference axis and with the Y axis drive means including three drive elements located at 90xc2x0, 210xc2x0 and 330xc2x0 with respect to the fixed reference axis, which X and Y axis drive and pick off elements are operable to detect and nullify the response mode motions.
Alternatively, the carrier mode is an in-plane Cos 3 xcex8 mode, with the carrier mode drive means including three drive elements located at 0xc2x0, 120xc2x0 and 240xc2x0 with respect to a fixed reference axis in the plane of the resonator, with the carrier mode pick off means including three pick off elements located at 60xc2x0, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis, wherein the X axis response mode is a Cos 2 xcex8 mode, with the X axis pick off means including two pick off elements located at 0xc2x0 and 180xc2x0 with respect to the fixed reference axis, with the X axis drive means including two drive elements located at 90xc2x0 and 270xc2x0 with respect to the fixed reference axis, and wherein the Y axis response mode is a Sin 2 xcex8 mode, with the Y axis pick off means including two pick off elements located at 45xc2x0 and 225xc2x0 with respect to the fixed reference axis and with the Y axis drive means including two drive elements located at 135xc2x0 and 315xc2x0 with respect to the fixed reference axis.
Conveniently, the carrier mode is an in-plane Cos 3 xcex8 mode, with the carrier mode drive means including three drive elements located at 0xc2x0, 120xc2x0 and 240xc2x0 with respect to a fixed reference axis in the plane of the resonator, with the carrier mode pick off means including three pick off elements located at 60xc2x0, 180xc2x0 and 300xc2x0 with respect to the fixed reference axis, wherein the X axis response mode is a Cos 4 xcex8 mode, with the X axis pick off means including four pick off elements located at 0xc2x0, 90xc2x0, 180xc2x0 and 270xc2x0 with respect to the fixed reference axis, with the X axis drive means including four drive elements located at 45xc2x0, 135xc2x0, 225xc2x0 and 315xc2x0 with respect to the fixed reference axis and wherein the Y axis response mode is a Sin 4 xcex8 mode, with the Y axis pick off means including four pick off elements located at 22.5xc2x0, 112.5xc2x0 and 292.5xc2x0 with respect to the fixed reference axis, and with the Y axis drive means including four drive elements located at 67.5xc2x0, 157.5xc2x0, 247.5xc2x0 and 337.5xc2x0 with respect to the fixed reference axis.
Advantageously, a gyroscope for sensing rate of three axes, includes Z axis response mode pick off means for sensing in-plane Sin 2 xcex8 response mode movement of the resonator, which Z axis pick off means includes two pick off elements located at 45xc2x0 and 225xc2x0 with respect to the fixed reference axis, and including Z axis response mode drive means having two drive elements located at 135xc2x0 and 315xc2x0 with respect to the fixed reference axis.
Preferably, a gyroscope for sensing rate on three axes, includes Z axis response mode pick off means for sensing in-plane Sin 3 xcex8 response mode movement of the resonator, which Z axis pick off means includes three pick off elements located at 90xc2x0, 210xc2x0 and 330xc2x0 with respect to the fixed reference axis, and including Z axis response mode drive means having three drive elements located at 30xc2x0, 150xc2x0 and 270xc2x0 with respect to the fixed reference axis.
Advantageously, the resonator is made from metal, quartz, polysilicon or bulk silicon.
Advantageously the drive means and the pick off means are electrostatic, electromagnetic, piezoelectric or optical.